Imaging modalities and physics: truncation artefact in MRI: practice question

A Radiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Radiology · Imaging modalities and physics: truncation artefact in MRI

Sample item

A sagittal cervical spine T2 MRI acquired with a coarse phase-encoding matrix shows a thin central line of high signal in the cord. On a repeat with a finer matrix the line disappears and the cord is normal. What is the explanation?

APhase-encoding wraparoundBGibbs (truncation) ringingCMagnetic susceptibility distortionDChemical shift misregistration

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Gibbs (truncation) ringing

Gibbs ringing appears at sharp high-contrast boundaries, such as the cord and CSF, because the data are truncated. It can mimic a syrinx and is reduced by increasing the matrix or applying filtering.

Option by option

A. Phase-encoding wraparound
Wraparound folds anatomy outside the field of view onto the image and does not draw a line within the cord.
B. Gibbs (truncation) ringing (correct)
Correct. Truncated sampling produces parallel lines at a sharp interface, simulating a syrinx.
C. Magnetic susceptibility distortion
Susceptibility artefact causes signal loss and distortion near metal or air, not a thin line inside the cord.
D. Chemical shift misregistration
Chemical shift misregistration creates paired bright and dark bands at fat-water borders in the frequency direction.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is B, Gibbs (truncation) ringing. Gibbs ringing appears at sharp high-contrast boundaries, such as the cord and CSF, because the data are truncated.

Why is "Phase-encoding wraparound" not the answer?

Wraparound folds anatomy outside the field of view onto the image and does not draw a line within the cord.

Why is "Magnetic susceptibility distortion" not the answer?

Susceptibility artefact causes signal loss and distortion near metal or air, not a thin line inside the cord.

Why is "Chemical shift misregistration" not the answer?

Chemical shift misregistration creates paired bright and dark bands at fat-water borders in the frequency direction.

What concept does this question test?

It tests Imaging modalities and physics: truncation artefact in MRI in Radiology. It can mimic a syrinx and is reduced by increasing the matrix or applying filtering.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Imaging modalities and physics: truncation artefact in MRI?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.